Welcome to your interview.
The question is on your right: Flatten Nested JavaScript Objects. Take a moment with it first.
Talk your thinking through with me if you like - when you're confident, submit your answer and I'll grade it like a real screen (7/10 or better passes). Discussion and graded submissions share your five interviewer interactions, so spend them well.
Write a flatten function that recursively converts a deeply nested JavaScript object into a flat key-value mapping using depth-first search.